Low Level Format, UMask and Some Important File Settings

Low Level Format:

The command ‘shred’ is used for low level format 25 times; we can’t recover files after this

#shred /dev/hda

 UMask:-

User Mask

Default value for root = 0022

Default value for users = 0002

When we create any new file. The default value will be 666. in this case Umask means 666-002 = 664 for normal user and for the root the default value will be 666-022=644

The default value for a directory is 777. in this case umask means that whenever we create new directory, the default valkue for normal user 777-002 = 775 and for root, the default value 777-022 = 755

Some Important File Settings:

GRUB.CONF

GRUB stands for GRand Unified Bootloader. It is the default boot loader used by Red Hat Linux…… Grub.conf file found in /boot/grub/grub.conf

If remove grub file :--------- boot from cd and go to linux rescue.

grub>find   /grub/stage1

         (hd0,1)

grub> root   (hd0,1)

grub>find  /etc/passwd

         (hd0,2)

grub> kernel  /vmlinuz-2.6.18-8.el5 ro root=/dev/hda3

grub>initrd  /initrd-2.6.18-8.el5.img

grub>boot

after booting system open grum file and enter grub entery…

#vi /boot/grub/grub.conf

Default = 0

Timeout = 5

Splash image=(hd0,0)/grub/splash.xpm.gz

Hidden menu

Title Redhat Linux

Root (hd0,0)

Kernel /vmlinuz-2.6.18-8.el5 ro root=LABEL=/ rhgb quiet

Initrd /initrd-2.6.18-8.el5.img

2.INITRD

If remove initrd file how to recover

Boot form cd and goto linux rescue and write this command..

#mkinitrd  -v   /boot/initrd-$(uname  -r).img   $(uname  -r)

#exit

#exit

3. INITTAB

Run level setting are done in inittab file. Inittab found in

/etc/inittab

#vi /etc/inittab

id:5:initdefault:

si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0

l1:1:wait:/etc/rc.d/rc 1

l2:2:wait:/etc/rc.d/rc 2

l3:3:wait:/etc/rc.d/rc 3

l4:4:wait:/etc/rc.d/rc 4

l5:5:wait:/etc/rc.d/rc 5

l6:6:wait:/etc/rc.d/rc 6

ca::ctrlaltdel:/sbin/shutdown –t3 –r now *

1:2345:respawn:/sbin/mingetty tty1

2:2345:respawn:/sbin/mingetty tty2

3:2345:respawn:/sbin/mingetty tty3

4:2345:respawn:/sbin/mingetty tty4

5:2345:respawn:/sbin/mingetty tty5

6:2345:respawn:/sbin/mingetty tty6

X:5:respawn:/etc/x11/prefdm –nodaemon

Setting Grub Password

Two method are used to set grub password

Method I:

#vi /boot/grub/grub.conf

Below

Hiddenmenu

Password = redhat

This password is not in encrypted form.

Method II: Encrypted form

#grub

grub>md5crypt

enter password : * * * *

after enter now you see password encryptions format

like this        ghs84hD1hd3gs42Kj4$3s   

now copy this encryption formatand open

new terminal and open grub file

#vim /boot/grub/brub.conf

paste in this cncryptions here two lines

password  --md5crypt ghs84hD1hd3gs42Kj4$3s   

title  Red Hat linux

password  --md5crypt ghs84hD1hd3gs42Kj4$3s

root (hd0,0)

:wq